In the operation of many chemical and other processes it is often necessary to periodically sample fluids which are flowing within the process at various points. Many process fluids present serious safety hazards when released or exposed to the atmosphere. Other process fluids, although not extremely hazardous or toxic, may be highly water sensitive for absorption of atmosphere moisture which makes it impossible to obtain an accurate moisture analysis if the sample is exposed to the atmosphere. For a multitude of reasons, it is desired to obtain various process fluid samples in a closed loop manner which does not permit exposure of the sample fluid to the atmosphere.
Heretofore, a variety of devices and mechanisms have been disclosed for the purpose of obtaining closed loop samples. U.S. Pat. No. 2,693,705 discloses a liquid sampler for the sampling of radioactive, poisonous or valuable liquids for analytical purposes. This patent discloses a sampler device by which, through the operation of an air pressure aspirator, a sample is drawn by aspiration from a sample point through an injection needle into a septum closed sample container and liquid overflow beyond a preset sample amount are aspirated from the sample container back into the line from which the sample is taken. A closed loop sampler of this design requires a source of pressurized air for its proper operation and is generally designed for small sample volumes.
Other closed loop sampling devices which have heretofore been described utilize the pressure of the sample in the sample line as the driving force by which a liquid sample is propelled into the sample container. In the design disclosed by U.S. Pat. No. 4,174,632, there is disclosed a closed loop sampling device comprising a valve having integrally formed with the body thereof a cap which receives a sample container the external surface of which corresponds to the internal configuration of the cap, an injection needle is disposed within the cap and is in fluid communication with the valve. A sample is taken by moving a sample container having a septum closure through the open end of the cap, the cap properly positions the container for penetration of the septum, and pressing it upwards against the injection needle to penetrate the septum. When so configured the valve is turned on into communication with the needle and the sample passes from the line through the needle into the sample container. For purposes of venting the sample container as it fills with liquid, a second or vent needle may be provided within the cap which communicates vented vapor back to the process or to a special storage area. In such a device as disclosed, because the cap is integrally formed with the valve body, should a sample needle or a vent needle become clogged and need cleaning or replacement, the entire sampling device comprising the valve with integrally formed cap and needles thereof requires replacement. Further, because the cap is integrally formed with the valve body, the sampler is specific to a single size of sample container.
U.S. Pat. No. 4,887,472 discloses a closed loop sampler which in part comprises a hood having a sampling and venting needle integrally formed therewith, one end of said hood is thread mounted to a valve, the other end of said hood is mounted with a reciprocating sleeve which receives a septum closed sample container, the lower end of the said hood is itself sealed with a septum. A sample is taken by reciprocating the sleeve with sample container upward towards the valve causing the two needles to penetrate the first septum which seals the hood itself, and further the septum of the sample container. The valve is then operated, a sample taken and upon completion of the sample, the sleeve is reciprocated downward whereby the needles are withdrawn from penetration of the septum of the sample container as well as the lower septum of the hood. A fluid may then be circulated into the sealed area around the needles defined by the lower septum of the hood and the needles washed of old sample before a new sample is taken. Again, because of the integral formation of the sample and vent needles with the hood, should one or both needles become clogged, it is necessary to replace the entire hood mechanism of this sampler.
In yet other closed loop sampler mechanisms as disclosed in U.S. Pat. Nos. 4,651,574; 4,791,821 and 4,879,915, a sampling device is disclosed, the key element of which is a unitary needle body having in a single needle stem a sample fluid passageway and a vent gas passageway. The sample fluid passageway communicates the needle tip to the valve whereas the vent passageway communicates the needle tip to a side location of the needle body which is internally threaded to receive a fitting connection. The upper portion of this needle body is threaded directly to a valve and to the lower portion of the needle body a sample container hood is threaded. A fluid sample is taken by passing a septum closed sample container through the lower end of the hood, pressing its septum against the needle stem and opening the valve until a desired amount of sample fluid is obtained.
Each of the types of closed loop samplers heretofore disclosed entail various disadvantages. The aspirated dual needle constant volume design of U.S. Pat. No. 2,693,705 requires the presence of an aspirator unit and a source of external compressed air, which both complicates and renders more expensive the design of such unit and its operation. In the sample devices of U.S. Pat. Nos. 4,174,632 and 4,887,472, the sample and vent needles are not separately serviceable for repair/cleaning or replacement. Further, when installing such a sampler, the proper positioning of the vent gas port is obtained in the case of the '632 design by reason of its manufacture as an integral part of the valve. In the design of the '472 patent, since the hood element carries the ventway passage port and the hood element is itself directly threaded to the valve, proper positioning of the vent gas port is a matter of proper thread design of the threaded portion of the hood body. That is, the valve fitting threads must be designed to secure a fluid tight fastening of the hood to the valve body at a point wherein when proper fastening is obtained, the vent passageway port is properly positioned. Accordingly, this renders the manufacture and on site installation of such device to be more difficult. In the dual passageway, single needle body design of U.S. Pat. Nos. 4,651,574; 4,791,821 and 4,879,915, the needle stem must be of a sufficiently large diameter to accommodate the two passageways therethrough. This, unfortunately, renders penetration of the septum of the sample container to be more difficult and further introduces a larger than desirable perforation to the septum which may not properly reseal upon removal of the sample container from the needle stem.
Further, by and large, such closed loop sampler devices as have heretofore been disclosed require custom installation by the process operator. That is, the user of the device is required to custom install the device with the necessary sample fluid conduit line and the vent gas conduit line. The installation of a plurality of even the same types of a device throughout a process unit often lacks any degree of uniformity.
It is desirable to develop a closed loop fluid sampling device which permits sampling of fluid flow within a process line without the need for a separate pump or aspirator as a part of the device; which permits ready removal, repair and replacement of the sample and/or vent needles of the device; permits of the sample/vent needles to be constructed of a different material from other non-wetted parts of the device; which allows for the taking of samples of differing volumes as desired; and which eliminates or reduces dead volume within the device wherein a portion of processes fluid taken from a previous sample may be held up within the device to contaminate a new portion of process fluid when a subsequent sample is taken. It is further desired to develop a self-contained sampling system unit which is adapted to easy and uniform installation by the simple expedient of positioning and line fitting connection of the unit at a sample point within a processing unit.